The pattern followed here is, 1st number x 4 = 2nd number. 3rd number x 4 = 4th number. For, 4 : 16 4 : 4 x 4 Similarly, 5 : ? 5 : 5 x 4 5 : 20 '20' is related to the third number in the same way as the second number is related to the first number. Hence, "20" is the correct answer.